Seven of President Donald Trump's eight border wall prototypes are shown near completion along US- Mexico border near San Diego, California on October 23, 2017. Reuters/Mike Blake

Questions are lingering around the mysterious death of Rogelio Martinez, a border patrol agent who died in Texas last weekend after sustaining severe injuries.

Investigators have said they're looking into whether a "potential assault" occurred, but cannot rule out the possibility it was an accident.

The incident has become a flashpoint in the ongoing debate over President Donald Trump's long-promised border wall.

FBI officials said Tuesday they were investigating a "potential assault" that may have led to the death of a border patrol agent in southwest Texas last weekend, but they added that they could not rule out another cause of death.

The mysterious case of 36-year-old Rogelio Martinez's death has prompted frenzied speculation that an ambush took place, perhaps at the hands of undocumented immigrants or drug traffickers, though officials have cautioned that the details around the death are hazy and they have not yet reached conclusions.

Officials from the federal Customs and Border Protection agency have said that Martinez and his fellow agent were "responding to activity" near a drainage culvert along Interstate 10 in Van Horn, Texas around 4 a.m. on Sunday when they were somehow hurt. Martinez's partner then called for help and the pair were taken to a hospital, where Martinez later died from his injuries.

Authorities said another agent, who has not been identified, was also seriously injured in the incident, and both men suffered traumatic head injuries and broken bones.

"We call it potential because we do not yet have the full picture yet as to what transpired," FBI Special Agent-in-Charge Emmerson Buie Jr. said at a press conference at the FBI's El Paso office. He added that the bureau is offering a $25,000 reward for information that could lead to the case being solved.

Roy Villarreal, acting Chief Patrol Agent of the Border Patrol, San Diego Sector, left, speaks during a news conference as other Border Patrol agents look on in front of secondary fencing along the border separating San Diego from Tijuana, Mexico, Tuesday, Sept. 26, 2017, in San Diego. Associated Press/Gregory Bull One US official familiar with the investigation, however, told the Associated Press on Monday that investigators believe Martinez and the other agent may have sustained their injuries by falling into the culvert. The official added that Martinez's partner has no recollection of the incident.

The local sheriff in Culberson County, where the incident occurred, also appeared skeptical that an attack was the cause of the injuries and death.

"The evidence is not obvious as to what happened out there," Sheriff Oscar Carrillo told the Dallas Morning News.

'We will build the Wall!

The National Border Patrol Council, the labor union representing the agents, has described the incident as an "ambush" and told media that Martinez died of blunt force trauma to the head.

"I have been told by several agents that it was a grisly scene, and that his injuries were very extensive," council president Brandon Judd told The Washington Post. "We believe he was struck in the head with rocks, or multiple rocks."

But despite the questions still surrounding Martinez's death, Texas politicians have presumed that a crime occurred. Gov. Greg Abbott and Sen. Ted Cruz, both Republicans, have described the incident as an "attack."

"This is a stark reminder of the ongoing threat that an unsecure border poses to the safety of our communities and those charged with defending them," Cruz said in a statement.

President Donald Trump also seized on the death, which he suggested on Twitter was a criminal matter, as evidence of the pressing need for his long-promised wall along the US-Mexico border.

"Border Patrol Officer killed at Southern Border, another badly hurt," he said. "We will seek out and bring to justice those responsible. We will, and must, build the Wall!"

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